In general, capacitors are electrical devices capable of storing or absorbing electrical charges in time. Decoupling capacitors disposed near power/ground pins of electronic devices may be used to reduce undesirable noises. For example, surface mounted devices (SMDs) or embedded structures on or in printed circuit boards (PCBs) may reduce undesirable noises. Decoupling capacitors provide a localized source of direct-current (DC) power for electronic devices as the signals switch simultaneously at high speed.
With increasing signal transmission speed in ICs, unexpected interference resulting from power noises, ground bounces or simultaneous switching noises (SSN) may be serious and therefore may not be neglected for designers. However, parasitic inductances induced by conductive traces may become higher for decoupling capacitors and power delivery systems as the electronic devices operate at a relatively high frequency. Accordingly, it is difficult for decoupling capacitors to stabilize power supply level.
Capacitors embedded or buried in a PCB, IC substrate or interposer layer, have been proposed to replace the SMD capacitors for eliminating switching noise. However, capacitors embedded in PCBs or the substrates of ICs, may also exhibit more inductive than capacitive properties when they operate at a frequency greater than its resonant frequency. That is, the impedance of the embedded capacitors may increase as the operating frequency increases, resulting in degeneration of the decoupling performance for a power delivery network. As a result, how to reduce the impedance of the embedded capacitors and broaden the decoupling bandwidth are the critical issues for power integrity design.